5F1 Champ(s) - too ‘dark’ & too compressed: How to fix?

Discussion in 'Glowing Bottle Tube Amp Forum' started by Wharfcreek, Sep 13, 2019 at 4:28 PM.

  1. Wharfcreek

    Wharfcreek TDPRI Member

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    So I’ve built a few repro kit Champs as well as a few clone units, and I’ve come to the conclusion that a ‘stock’ 5F1 when built to spec is almost lame! Granted it’s an iconic amp, but it truly lacks luster and is almost anemic by comparison to other modern day amps. I have a couple Epiphone Valve Junior Amps that scream circles around my Champs, any I recently was blown away by my friends Univalve amp. So in trying to narrow down my two biggest complaints about my stock Champ units, it boils down to simply being too ‘dark’ and too compressed. I’m wondering what others may think about theses comments, but also if anyone knows any common mods that might address either of these symptoms?
     
  2. EsquireBoy

    EsquireBoy Tele-Meister

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    I used to have a Fender Custom 57 Champ: it was nice, but it was indeed on the dark side of tone to my ears. Very very nice when pushed into overdrive, but too dark for me when played clean-ish.

    I traded it for a 5f2 tweed Princeton clone that has all the qualities I liked about the Champ, but that sounds brighter and more open.

    I suspect it has a lot to do with the speaker.
     
  3. irie

    irie Tele-Holic

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    are you sure you haven't shaved all the high frequencies off your hearing?

    I do not think the issues you are describing are the circuits fault. I find myself always having to roll back the tone knob on all of my guitars when I play champs.

    As far as compression goes, its 5 watts man, how much headroom do you expect it to have?
     
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  4. boredguy6060

    boredguy6060 Friend of Leo's

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    On the original 5F1 the input cathode resistor is unbypassed. If you have an old 5F1 or a kit that follows the exact layout of the original then it can seem kinda dull.
    However later versions had the input cathode bypassed with a 25uf/25v cap. This will definitely add some life to the 5F1 and give you plenty of grit.
     
  5. Guitarteach

    Guitarteach Poster Extraordinaire

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    Mine has switchable bypass caps on both halves of the preamp, a variable NFB and a VVR circuit.

    Tonnes of bright and dirt... so I added a tone control too.

    I play it through a 12” Celestion Blue which really opens it up.
     
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  6. drf64

    drf64 Poster Extraordinaire Silver Supporter

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    2 thoughts. The first is your speaker. I like AlNicos in tweeds. The second is, if you are so inclined, turn it into a 5F1X2. I love mine with a 10” emi legend 1028
     
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  7. muchxs

    muchxs Doctor of Teleocity

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    If you think a Valve Junior sounds better than a 5F1 you need to see an audiologist.

    Valve Junior versions 1 and 2 have built- in design flaws. They were designed by people who didn't even know enough to built a functional copy of an existing circuit.
     
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  8. akuster777

    akuster777 TDPRI Member

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    I've had success with brightening my 5f1 build, adjusting to my taste, one at a time: 1) to a vintage alnico speaker, 2) 10uf v1 cathode bypass cap, 3) 470pf silver mica bright cap on the volume pot, 4) .01uf v1a coupling cap, 5) 56k negative feedback resistor, 6) 16uf filter caps. Try some and listen to what works for you, then let us know what you like... Best wishes, Andrew
     
  9. RottenTheCat

    RottenTheCat Tele-Meister

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    Hard to give advice without knowing every single build detail
     
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  10. muchxs

    muchxs Doctor of Teleocity

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    Pretty easy to give advice knowin' what I know.

    Stock Valve Junior has a 68k grid stopper just like a Fender 5F1. The big enormous blatant screw- up is it also has a 68k grid leak. Grid stopper and grid leak form a voltage divider and shunt half of our guitar signal straight to the ground.

    … so those expensive pickups we have are relatively useless. Effectively, the Valve Junior is like having our guitar volume rolled off all the time.

    Next Valve Junior über stupid is the 1meg / 1meg voltage divider after the first gain stage. If it wasn't bad enough we were dumping half of our signal straight into the ground, this thing dumps half of it into the ground again.

    It's pretty easy to modify a 5F1 into a Version 1 or Version 2 Valve Junior. Like I said, the Valve Junior was designed by people who couldn't even build a functional copy of an existing circuit.

    What we can learn from the 5F1 / Valve Junior comparo:

    If we roll off our guitar volume our Champ will clean up (slightly) and play nice. That's how it was designed. It was designed as the companion amp for Fender lap steels, essentially really poor man's Esquires we played on our lap. We're supposed to roll the guitar volume off. Otherwise we get into all that yucky overdrive that was totally unacceptable in the 1950s. Telecasters and lap steels have tone controls. They're supposed to be relatively well thought out controllers for 1950s amps. IMO that's functionally what they are, relatively well thought out controllers for 1950s amps.

    Rolling the guitar volume off gets us out of the darkness. There's probably no need to touch the tone control with the guitar volume rolled off.

    That's the way Leo designed it and that's the way it works.
     
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  11. Wharfcreek

    Wharfcreek TDPRI Member

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    OK, as to 'getting my ears checked'......actually, Yea! I've done that! My HF hearing is in the upper 99%! I've been building Hi-Fi amps for the past 20 years..... and in the 10 years prior to that I was doing guitar amp repairs. It's only been in the last year or so that I've migrated back to guitar amps, mostly because I just got bored with the Hi-Fi stuff...... and some little 'kit' amp caught my eye from AES......so I bought it and built it. After that I built about 5 different 'clone' SE amps, all using varying component parts, but all based on the Tweed Champ or Princeton. I then built a complete 'replica' amp, again using varying parts; ie the ClassicTone power and output transformers, an replica Chassis from AES, a turret board from somewhere I can't even remember, and a replica cabinet that came from some vendor that Reverb was promoting. Then I bought the MoJoTone Kit. I also did a complete rebuild of an old Gibson G-4 Les Paul Junior amp. In all I now have about 15 of these little 'flea' amps.....and I think my 20 years of Hi Fi amp work qualifies me to at least have a valid opinion about tone and compression. I can't speak to every build of this circuit......as I'm sure they may all differ in one way or another. BUT....the exact copies that I built both have similar characteristics in that they lack suitable HF response, AND....the compression is so clearly notable that it's actually bothersome. And, when compared to something like either of my Valve Junior amps, I do NOT hear the same compression level, and I get a much greater sense of frequency response. So, say what you will about the shortcomings of the Valve Junior circuit. The proof is in how it sounds, not how it looks on paper! To back this up I've had some pretty competent musicians come and audition some of my builds, along with doing comparisons to my other amps. Invariably the VJ amp is found to be pretty impressive. One friend of mine who is a former PRS employee and now works for Knaggs guitars thought the replica Champ amps sounded terrible. Given all I did was build it, I wasn't too insulted. But, I've tried everything from 8" speakers, to 10"s, to 12"s, Alnico and Ceramic magnet types, Open and closed cabinets, and even a bit of 'external' processing. The bottom line is that built as designed, there is HF roll-off within the circuit, as well as some ill-effects of compression most likely at the pre-amp stage. I appreciate the suggestions to help address ways to alter this. I'll try some of them and report back. I have, for the record, done some bypassing, as well as played with the feedback level. One of my HiFi buddies suggested some changes to the plate and cathode resistors on the 12AX.... He ended up going with a plate resistor of like 47K, and 3.3K on the cathodes. According to him, the greatly reduced the compression he was having in his amp. Anyway.....onward!
     
  12. Nickfl

    Nickfl Tele-Afflicted

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    I think your problem may be that you just don't like the way a 5f1 sounds, which is a perfectly valid opinion, I don't really like them either. Sometimes the best answer to the often asked "how can I make x amp sound better" isn't a modification to the circuit but just replace it with an amp you actually like.

    IMO the champ suffers irredeemably from the lack of a tone control and adding one (turning it into a Tweed Princeton) turns it into a completely different and vastly better amp.
     
  13. Ess Eff

    Ess Eff Tele-Meister

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    I kinda found the opposite with mine.

    No bypass cap = cleaner more headroom/less warm.
    .
     
  14. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    My Champ-a-like has no bypass caps on the pre-amp valve and fixed NFB ( 22K from the 4 Ohm tap )
    Is it a little dark?, it can be, at low volumes. Is it too compressed?, no. Not at all. Not until around 1/3rd of the volume sweep has been used does it begin to compress. At that point, it sings a sweet song. Warm, open and clear. Lively, responsive, rich and full of character. This continues up to around 2/3rd of the volume sweep, by which point it's snarling. Such a simple circuit. It responds to everything I do, and hides nothing.

    Mine is a WF-55, and it differs in a couple of minor ways from the classic Champ. It has a solid state rectifier, not that that makes a difference in an SE amp. Here's the schematic.

    ak00sc2.jpg

    I've played about with adding bypasses via croc-clips and careful balancing acts and adding a tone control in a similar fashion, but this circuit, as it stands, sounds utterly glorious to me. The WF-55 comes with substantial transformers. I don't hear what I think is transformer saturation until very close to the end of the volume sweep. I've built a second one, to 5F2a-ish specs, and found I needed to bypass v1a else it became rather flaccid at lower volumes.
    I do not want for treble. Maybe a bypass cap on the volume control would help at lower volumes for you?
    I've tried the Valve Junior, in its first and final guises, and fail to hear why anyone would want one in stock form. I too enjoy building Hi-Fi and guitar amps, much to the consternation of my wife, and she really likes the sound of my Champ-a-like. Maybe the Champ just isn't for you, as the VJ isn't for others?
     
  15. muchxs

    muchxs Doctor of Teleocity

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    :D :D :D

    Told you exactly why your Valve Junior doesn't compress as much as your 5F1. It's simple... if you piss your signal into the ground, your signal can't drive the circuit as hard as it otherwise might have. It's a basic concept in hi-fi. "Don't use all of it if you want to stay clean."

    Hi-fi gear has built- in and redundant "Don't use all of it."

    The quick 'n' (not as) dirty is don't run your 5F1 at 10 / 10ths. The easy way to do that is to simply roll off your guitar volume.

    Perhaps. Although... I rarely come across a hi-fi enthusiast with an ugly rig.

    Electronics design is like the Hanon exercises for piano. Hanon was carefully thought out to eliminate goofy reaches. A piano is a very efficient machine when used as it was intended. I've seen pianists who take "shortcuts" and then are stuck with the shortcut long after it gets in the way of efficient musicianship.

    The Valve Junior is like that. Almost nothing is as it should be in those things.
     
    Last edited: Sep 14, 2019 at 10:56 AM
  16. RottenTheCat

    RottenTheCat Tele-Meister

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    The speakers we use today are better than the speakers used "in the day". I'm wondering if just adding the bright cap... something small like 120pf.... across the volume control.

    A note on bright caps: A lot of folks like silver mica, I'm shying from them for bright caps on volume controls, sometimes shying from 'em on the treble control of the Fender style Baxandall tone control. Reason being is the relative resistance of the silver mica caps is pretty low compared to the ceramics. The ESR being so low sometimes gives you too much of a good thing. Put another way, the value in pf's gives you the frequency at which the bleed (or treble) will work, but the ESR will, more or less, give you the "amount". Sometimes... really commonly, I find 100pf or 120pf, then 50pf, then 180pf... all get tried and somethings just "missing" from the desired response. Go back with ceramic and the 100pf or 120pf seems to do it.

    Just passin that along for general consideration ;)
     
  17. bblumentritt

    bblumentritt Tele-Afflicted Platinum Supporter

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    I had an original tweed Champ - I think it was a '59 but I really don't remember. Back in the early 1980's I had a brand-new Strat. For years I called that combination the best tone I ever got, an impression I had from a gig I did backing a singer-songwriter.
     
  18. wrathfuldeity

    wrathfuldeity Tele-Afflicted

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    I have no idea how to fix....but I do know that Muchxs does...because I scored a seafoam champ with an alnico 6x9 of his off CL and it is absolutely amazing. It's responsive to the git's pu, tone/volume and plays great with pedals.
     
  19. Wharfcreek

    Wharfcreek TDPRI Member

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    I guess I come from the 'amp camp' that simply turns the amp on and turns every control to max, and then plays it. That said, I'm not including the 'effects' controls like tremolo, vibrato, or reverb. If the amp had a master volume, I might play around with trying to find a sweet spot between input volume and master volume. But, something like this little Champ is, to me, something that could actually be built with no volume control at all. Just bypass that 1M pot and put a jumper in there!! Anyway, I've spent a bit more time today playing with some of my clones as well as with the two replica amps. One of the two is basically build 100% to spec with the exception of having an 8 ohm / 5K PI output transformer in it. That amp also had the feedback resistor, the former 22K value, replaced with 30K made up of a 27K and a 3.3K in series. In doing the math, the feedback value is to be multiplied by 1.4 or so to compensate for the change in secondary output from the output transformer. So, 22K X 1.4 = 30.8. The series value of the 27K and the 3.3K = 30.3. Given a 5% tolerance margin, 30.3 is close enough to 30.8 to be 'in spec' for the change. One comment here is that both my 'replica' amps are using ceramic magnet speakers. The MoJo version has a Warehouse G8C in it, and the other has a Jensen C8R. Both of these are NEW..... and perhaps do have some affect on this 'dark' issue. I say that because I took one of my 'clone' amps, which are all just amps on chassis builds, and played it for a while today as well. However, I used two other cabinets that I have when using that amp. One cabinet is a Crate V5 unit where the amp has been removed and the crate speaker has been replaced with some old Jensen. The other cabinet is an old Peavey cab from some little 10 or 15 watt practice amp. It originally had an 8" speaker in it as well, but I got the cab 'empty', so I pulled the baffle board and replaced it with some 3-ply 3/8" plywood and mounted an old 8 ohm 10" alnico speaker in it. This speaker originally came out of some accordion amp I was told, but where ever it came from, it really sounds good with my little amp. I'll add that this particular clone amp uses an EL84 instead of the 6V6, and a 6CA4 instead of the 5Y3. I also added a 4uf cap right off the rectifier socket and put a small 2H / 100ma choke in it. Then first stage filter cap is 22 uf, then the final two are 16 instead of 8. So, like I said...... a 'clone', but not a 'copy'. Anyway, being played through the little Peavey or Crate cabinets, that amp sounds WAY better!! So, I'm going to try the two replica amps tomorrow and play them through those two cabs and see is my impressions change. Bottom line: I ordered a couple Alnico speakers today off ebay. Maybe that will cure some of this. One last comment: my little clone has a LOT more 'life' in it....and could draw some feedback between the amp and the guitar.....and really 'felt' like a 'big' amp! So....I know there's hope for these replica amps. Just not sure yet how to get there. And, btw, I'm reading each and every comment and taking it all in. Please do be upset if I didn't respond to any one of them directly. I tend to let stuff sink in prior to 'engaging' ...... as some times my mind or impressions about a comment does change!! So, again, thanks to everyone for responding!! I think in the end I'll come up with some valid perspectives for potential changes that will make this amp more to my liking. Not saying they will be good for anyone else, but perhaps a few out there may wish to follow my lead when I complete them and see if the alterations enhance their own amps!! Tom D.
     
  20. jrblue

    jrblue Tele-Afflicted

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    Wharfxs describes these amps accurately, IMO. Playing a Champ dimed, particularly with hot pickups, will sound crappy because that is how the amp works. Don't run it, or your guitar, full blast. (I don't know where the maxed-out approach came from to begin with, since it makes zero sense to operate an amp, or virtually any device ever made by humans, at the extreme all the time.) If your amp is not loud enough with both guitar and amp not maxed out on the volume controls, then your amp is too small for your usage. Get a bigger amp. The various mods to various Champs are all well known and mostly easy and the results are predictable in terms of tone. If your speaker doesn't suit the sound you want, change it for one that does.
     
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